How to store local data after user delete my iOS app?

[eggerr]

* NOTICE *
IT IS NOT AN AD! I'm in China, I don't know the developers!

I thought it's impossible, because all the data store in a sandbox, when user delete the app, all the data should be removed from the device.

But somehow, this happened:

I downloaded a wallpaper app from the appstore. < HD Wallpapers Stand > ( AGAIN, NOT AN AD )

It's a free app, if you don't pay, you can download limited wallpapers, up to 105.

I download a wallpaper and save to my album. it's now 1/105.
I delete the app, and delete the wallpaper in my album.

I turn off the iCloud backup function. OK, It's totally removed from my device, right?

I download it again.
I enter flight mode, so there is no internet connection.
I open the app, no wallpaper preview can be download from internet.

But the save count shows 1/105!

I'm not trying to steal their wallpapers, I did not change my wallpaper for 4 months. I just wanna know, how can this app know I saved 1 wallpaper already?

I delete the app. so it's not store in the app documents or tmp folder.
I delete the wallpaper in my album, SO it can't get it from an MD5 of my album.
I am in flight mode, so it can't get it from their server or anywhere on the internet.

Anyone knows where this app stored the save/download count?

[Duncan C]

Originally Posted by eggerr

* NOTICE *
IT IS NOT AN AD! I'm in China, I don't know the developers!

I thought it's impossible, because all the data store in a sandbox, when user delete the app, all the data should be removed from the device.

But somehow, this happened:

I downloaded a wallpaper app from the appstore. < HD Wallpapers Stand > ( AGAIN, NOT AN AD )

It's a free app, if you don't pay, you can download limited wallpapers, up to 105.

I download a wallpaper and save to my album. it's now 1/105.
I delete the app, and delete the wallpaper in my album.

I turn off the iCloud backup function. OK, It's totally removed from my device, right?

I download it again.
I enter flight mode, so there is no internet connection.
I open the app, no wallpaper preview can be download from internet.

But the save count shows 1/105!

I'm not trying to steal their wallpapers, I did not change my wallpaper for 4 months. I just wanna know, how can this app know I saved 1 wallpaper already?

I delete the app. so it's not store in the app documents or tmp folder.
I delete the wallpaper in my album, SO it can't get it from an MD5 of my album.
I am in flight mode, so it can't get it from their server or anywhere on the internet.

Anyone knows where this app stored the save/download count?

It probably creates a shared keychain entry.

If your company has 2 apps, with the bundle name

com.companyname.appfamily.app1

and

com.companyname.appfamily.app1

You can save entries in your keychain under

com.companyname.appfamily

That will be readable from either app. I don't think such keychain entries are deleted, even if you delete all the apps in that app family.

[eggerr]

Originally Posted by Duncan C

It probably creates a shared keychain entry.

If your company has 2 apps, with the bundle name

com.companyname.appfamily.app1

and

com.companyname.appfamily.app1

You can save entries in your keychain under

com.companyname.appfamily

That will be readable from either app. I don't think such keychain entries are deleted, even if you delete all the apps in that app family.

This is possible, but it's the only one I install on my iPhone, I don't have any other app from this developer.

So, it still unsolved

[Duncan C]

Originally Posted by eggerr

This is possible, but it's the only one I install on my iPhone, I don't have any other app from this developer.

So, it still unsolved

I believe the that shared keychain Id works even when there's only one app.

[eggerr]

Originally Posted by Duncan C

I believe the that shared keychain Id works even when there's only one app.

Thank you Duncan C, problem solved!

Uninstalling an application will not remove the items from the keychain. If you run the demo application on your device, and uninstall the app, the username and password will remain in the keychain (a firmware reset will, of course, remove the keychain values).

[Duncan C]

Originally Posted by eggerr

Thank you Duncan C, problem solved!

Care to explain? It might help others.

[foobar205]

I think that I have another question connected with topic but that can't be explained by shared keychain Id.

Some apps remember theirs notifications, location and twitter settings (or permissions) after reinstall. For example, I reinstalled Instagram app, and it remember all these settings (permissions). At the same time, another apps do not remember those stuff.